A circulator is in general a three-port device finding its place in all microwave systems, e.g. in AESA-systems and their associated Transmit/Receive-modules (T/R-modules) with the function to direct a signal flow from a transmitter to the antenna or to direct a signal flow from the antenna to the receiver. This is sometimes also described as switching between transmit and receive modes. The circulator can also have an additional function to work as a matching device between poorly matched functional blocks, e.g. as a matching device between the antenna and the transmitter or receiver. The circulator is located at the end of the T/R-module, close to the antenna. In addition to the circulator component there are also separate components as the power amplifier, PA, for the transmitted signal and the low noise amplifier, LNA, for the received signal. All these three components, often called a front-end arrangement of the T/R module, require a substantial area on a circuit bord.
By tradition the circulator itself is a design, based on ferrite disks and a bias magnet. This building practice result in a large occupying area with special mounting requirements. In addition it attenuates RF signals. Ferrite based circulators are also narrowband components occupying a large building area (Area=250−400 mm2). Together with the PA and LNA components, the area of this solution for a front-end arrangement is large. When the term RF-signal is used it includes all types of microwave signals.
FIG. 1 shows a conventions front-end arrangement with a Power Amplifier, PA 101, connected to a first port 102 of a circulator 103. A second port 104 of the circulator is connected via a limiter 105 to a Low Noise Amplifier, LNA, 106. A third port 107 of the circulator is connected to an antenna 108. The circulator is thus a three port device connecting the PA to the antenna when the antenna is working in the transmit mode and connecting the antenna, via the limiter, to the LNA when the antenna is operating in the receive mode. The limiter is protecting the LNA from high amplitudes of receievd energy.
US 2009/0286492 A1 presents a solution where the circulator is replaced by a semiconductor switch using Gallium Nitride (GaN) transistors. This solution however requires a separate component for the switch and at least one component for the LNA and PA, thus taking up a large building area.
There is thus a need for a solution providing a front-end arrangement for T/R-modules with at least reduced size and weight.